Tubes, valves, seals, containers, tanks, receivers, pressure vessels, pipelines, rigid conduits, flexible hoses or conduit, heat exchangers, and other similar fluid control components, are typically configured to retain, direct and/or transport fluids under pressure. These components may be assembled into a wide variety of pressurized fluid systems that include systems for operating blowout preventers, mud systems, hydraulic systems, high pressure air systems, steam systems, and the like.
One representative example of a pressure system is a pipeline for transporting natural gas or other hydrocarbons. Another example is a natural gas and/or oil well and/or wells of other types, whether being actively drilled or already producing. These wells typically transport fluids from the producing geological formation to a well head. Oil and gas wells include one or more of the following components: a Christmas tree or well head; production tubing; casing; drill pipe; blowout preventers (BOPs); completion equipment; coiled tubing; snubbing equipment; and other similar and typical components. Yet another example includes hydraulic and fuel lines of various types for transporting fluids for use in mechanical devices. Storage containers for retaining fluids therein and pressure systems which include additional types of fluid control components may also fall within the scope of this disclosure.
The fluids retained or transported within pressure systems typically include one or more gases, liquids, or combinations thereof, including any solid components entrained within the fluid. As one representative example, a typical fluid may include methane or natural gas, carbon dioxide, hydrogen sulfide, natural gas liquids, water, and nitrogen. Another example of a fluid in a pressure system, crude oil coming from a well typically includes methane, propane, octane, and longer-chained hydrocarbons, including heavy oil/asphaltenes. Yet another example is hydraulic fluid within a hydraulic line.
Pressure systems and the individual components that comprise the system, typically are tested to ensure the pressure system is capable of maintaining pressure integrity and that the pressure system is not leaking. For example, a pressure system typically is tested to provide assurance that the fluid system is capable of retaining the fluid held therein at a selected pressure (e.g., a maximum pressure rating or maximum rated pressure which can be 110%-150% of normal operating pressure) without the fluid leaking or escaping from the pressure system.
It is understood that in connection with liquids, gases and mixtures thereof which exhibit a potentially significant change in pressure as a function of the fluid's temperature, it can be difficult to determine whether a change in pressure, typically, although not necessarily, a decrease in pressure, in a pressure system is merely a result of the change in temperature of the fluid, or if it is a result of a leak somewhere within the pressure system.
By way of example, the pressure of a volume of a drilling fluid in a fixed container or pressure vessel used in oil and gas drilling can vary significantly with temperature. In deepwater offshore drilling in which the drilling fluid is stored at a temperature of between 80° F. to 120° F. at the surface, for instance, the temperature fluctuations can be quite large. The drilling fluid cools as it passes from the drilling platform, through drill pipe and/or the riser that is surrounded by the ocean, to a wellhead or blow-out preventer that can be several thousand feet below the surface of the ocean and on the sea floor where the ambient, surrounding water temperature might be as low as 34° F. Thus, there can be a large and rapid transfer of heat energy from the drilling fluid, through the containing drill pipe and/or riser, to the surrounding ocean, which, in turn, causes a sometimes significant decrease in both the temperature and the pressure of the fluid held within the pressure system. Consequently, it can be difficult to distinguish a drop in pressure caused by the decrease in temperature from a drop in pressure caused by a leak within the pressure system that is allowing the fluid held therein to escape.
To solve this problem of distinguishing the cause of the drop in pressure, operators of pressure systems frequently hold a test pressure within the pressure system for a significant period of time, ranging from 10 minutes to well over an hour, to allow the temperature of the fluid to stabilize and to reach what is essentially or effectively steady-state test pressure (i.e., one in which the test pressure changes very little with time). That is, it may be only after a steady-state pressure is reached that an operator might be assured that a decrease in pressure was a result of the fluid cooling via a transfer of heat from the fluid to the sea and/or other surrounding media rather than because of a leak.
In addition, tests may be repeated several times to rule out various factors that affect the test results, such as how steadily the test fluid is added, mistakes in the test procedure, additional confirmation for assurance, and the like. The result is that significant and, often unnecessary, time is spent performing the leak/pressure tests. A typical series of pressure tests required to test multiple components may often take from 12 to 24 hours to complete, which can become very expensive when, for example, an offshore drilling vessel or rig leases for $800,000 per day. Thus, significant savings in time and money can be made if a more efficient and accurate system and method of detecting leaks is found.
Other methods, including those that require complex integral and differential equations to form mathematical models that better fit observed data, have been proposed to reduce the time it takes to conduct a leak/pressure test. However, these modeling techniques typically rely on the accurate entry of numerous details of the pressure system, meticulous test protocols that must be strictly adhered to, and highly trained personal. Consequently, such methods are not practical and may often be unreliable.
Thus, there exists a need for a system and methods for quickly and accurately performing a leak/pressure test for a pressure system, particularly for a pressure system containing a fluid that demonstrate a significant change in pressure with a change in temperature, that is simple, and does not require complex models or extensive data to solve differential equations.